Tuesday, September 07, 2010

Since its arrival on the 3rd, this low from the Bay has lingered on in the Orissa region for the last 4 days, without any significant movement, and throwing all forecasts into the bin.From 1002 mb yesteday, it has become marked at 1000 mb on Tuesday evening.On Tuesday evening, it is stationary over Orissa (Thai map), and in this constant position, has precipitated very heavy rains in regions south/south west of the low in the last 2 days. Regular formation of thick clouds were seen in the Vidharbah/Chattisgarh and west M.P. areas due to this position hugging system !Rains, in the these areas, were as much as 222 mms were recorded in Brahmapuri (Vidharbha) today, Jabalpur 106 mms yesterday, and Jalpaiguri 210 mms on Sunday. Regions in Rajasthan were receiving very heavy rains, with flooding threats to the Kota area. The hill states of Utteranchall and H.P. have been getting good rainfall. Tehri recieved more than 125 mms yesterday, and Simla around 100 mms in the last 2 days. (IMD map of last 2 days).

It is time now for the system to move ! All forecasts aside, ( by the way, the low is now embedded in the monsoon axis), it is now supposed to move along the axis corridor (see IMD map), and travel north-west. Since it is now 1000 mb strength, I suppose it will survive till north M.P. region.

By the 9th. a pulse from the system will travel west towards Gujarat, and form an UAC, which will precipitate heavy rains in Gujarat and north interior Mah.

Later, due to the system's westward movement, southern coast of Sindh including Karachi can expect showers on Saturday/Sunday.

The coastal regions of South Gujarat and North Mah. should get heavy rains on the 9th/10th.

Bharuch district can expect some heavy rains from Wednesday evening and Thursday.

Off shore trough will keep the rains active along the rest of the western coast till the 10th.

There was some misunderstanding in reading my last blog of 4th. A reader from Gujarat questioned if the monsoon was in its last week now.The 200 hpa winds jet stream has turned complete westerly above the 30N areas. This is still the initial step of monsoon withdrawal.

In a normal time frame, from todays situation, the south-west monsoon can withdraw from west Rajasthan in a week's time. That is when you may see the jet streams in a westerly direction over the North-West regions.Systems are generally guided by these jet streams for their tracking directions. In the post monsoon period, we will see the westerly jet streams covering the whole peninsula, north of 10N. And the winter systems from the North move westwards.

Mumbai: Contrary to our forecast, Mumbai had some heavy showers on Monday night, and a few showers on Tuesday, with the rain guage reading 30 mms during Monday night and about 10 mms on Tuesday.Wednesday: Cloudy day, with rains intensity increasing from evening into the night. Precipitation amount expected till Thursday around 35 mms.Thursday: Overcast and cloudy with frequent rain showers. Rains decreasing after night. Rains expected around 35-40 mms.Friday: Skies will be partly cloudy, with heavy passing showers, of shorter durations.

Ocean signals indicate that the monsoon may be going into a weak phase from around the weekend.

It is about time too, according to Dr P.V. Joseph, eminent researcher and author on meteorology and a former director of India Meteorological Department (IMD).

RAINS FOR EAST

Speaking to Business Line on Monday, he said active monsoon conditions have been prevailing over the last two-week period.

This is normally the extent to which these conditions can sustain.

But it is the weak monsoon phase that paradoxically brings rains to East and Northeast India, which have been witnessing below normal rains right through the season.

Viewed in this context, the weak phase would go to ensure ‘spatially justified' pattern of rains by bringing rain where it matters most for the time being.

International models suggest that a monsoon-boosting Madden-Julian Oscillation (MJO) wave could set up clouding over Equatorial Indian Ocean and adjoining peninsular seas during the third week of September.

MJO waves ply in the upper levels of the atmosphere and have alternating dry and wet phases as they transit periodically from west to east.

NEXT MJO WAVE

The dry MJO phase invariably sets up the intra-season lean phases while the wet phase is responsible for triggering monsoon onsets and associated weather systems (low-pressure areas and depressions).

According to the Jones Model, the progressively weakening MJO phase will start reversing from September 18 before culminating in an active phase for five days from September 23.

The Empirical Wave Propagation method applied by the US National Centres for Environment Prediction (NCEP) says that it would be a largely MJO-neutral phase going forward before an essentially dry phase sets in by September 27.

The NCEP has forecast rains for mostly East India and parts of Central and Northwest India during the week ending September 13. But a big chunk of the rains are shown to fall over the Bay of Bengal waters.

OVERNIGHT RAINS

Meanwhile on Monday, an IMD update said that widespread rainfall was reported from Konkan, Goa and Coastal Karnataka during the 24 hours ending Monday morning.

It was fairly widespread over Himachal Pradesh, Uttarkhand, Haryana, west Uttar Pradesh, East Rajasthan, Gujarat, West Madhya Pradesh, Interior Maharashtra, Chhattisgarh, West Bengal, Sikkim and the Northeastern States.

IMD has had some ‘minor trouble' uploading links to some satellite products over the past few days.

It is in the process of retrieving the links, according to the office of the Deputy Director-General, Satellite Meteorology. But it refused to elaborate further.

A heavy rain warning for the next two days said that isolated heavy to very heavy rainfall would occur over Uttarkhand, West Uttar Pradesh and South Haryana in Northwest India.

Over the rest of Central and Peninsula India, the warning is valid over Orissa, North Coastal Andhra Pradesh, Telangana, South Chhattisgarh, Vidarbha, South Madhya Pradesh, Konkan, Goa, Coastal Karnakata, Sub-Himalayan West Bengal, Sikkim, Assam, Meghalaya and Arunachal Pradesh.

Extended outlook until Saturday spoke about the possibility of continued fairly widespread rainfall activity over most parts of the country outside of Interior Peninsular India, where it may be scattered.